Non-water cooled consumable electrode vacuum arc furnace for continuous process

ABSTRACT

A consumable electrode vacuum arc furnace and, more particularly, a direct current consumable electrode vacuum arc furnace is provided, wherein no water cooling is needed to cool down typically neither the electrodes, nor any other parts of the furnace, and this includes the shell, the flanges ports and the electrical connections of the furnace. The present furnace uses non-metallic electrodes, such as graphite electrode, which are suitable for melting metals, smelting of metal ores, and metal oxide to elemental metal where the use of graphite electrodes is a common practice. The present furnace and electrode assemblies render possible to perform a true continuous process of melting and smelting under controlled pressure.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims priority on U.S. Provisional Application No.62/858,883, now pending, filed on Jun. 7, 2019, which is hereinincorporated by reference.

FIELD

The present subject matter relates to vacuum arc furnaces and, moreparticularly, to sealed electric vacuum arc furnaces provided withconsumable moveable electrodes.

BACKGROUND

Electric arc furnaces have been used extensively in melting and smeltingprocesses. Particularly, vacuum arc furnaces have been used for meltingand re-melting applications where high quality and high purity of themetal is desired. For the applications in which a consumable electrodeis desired, such as in re-melting and smelting processes, theelectrodes' sealing is of great importance. In most cases, this resultsfrom the need, to control the arc voltage, for one or more electrodes tobe displaced constantly or intermittently. Moreover, when the electrodeis consumed during the process, it is mandatory to introduce a newelectrode to maintain a continuous operation. In the case of smeltingprocesses for metal production, such as silicon, the use of consumablegraphite electrodes is a common practice. Unlike the electrodes made ofmetals which have a perfect surface finish and very dense bulk, thosemade of graphite suffer from not possessing these properties, andspecifically since graphite possesses some degree of porosity which isdetrimental to reaching and maintaining high degree of vacuum levels.

Another aspect of vacuum-sealed electric arc furnaces lies in properlysealing the electrode that is displaced during the process. In general,sealing a moving object is more challenging than a stationary one. It isindeed the case when electrode cooling is avoided because the seal willbe exposed to higher temperatures. It is of great interest to avoid anywater cooling around the furnace since these furnaces operate at veryhigh temperatures and they contain molten metal and metal oxide.Therefore, any presence of water could cause a catastrophic failure ofthe furnace by steam explosion and consequently harm to the operators.Indeed, over the years, there have been many fatal accidents fromelectric arc furnaces, mostly due to water leakage.

In each of U.S. Pat. No. 2,971,996, which issued to Gruber et al. onFeb. 14, 1961, and U.S. Pat. No. 3,213,495, which issued to Buehl onOct. 26, 1965, a vacuum arc furnace with a consumable electrode isdescribed. The top electrode, which is the moving part, is sealed;however, the type of sealing is not provided, nor is the needed coolingand mechanical details of such sealing. The top electrode is connectedto a supporting rod with a different geometry passed through the topfurnace shell. It is evident that this design does not allow for acontinuous process where the electrode consumption has to be compensatedby introducing new electrode through the seal. Moreover, the cruciblebottom is water cooled, which increases the chance of water leaking intothe system, which can eventually cause a steam explosion.

In U.S. Pat. No. 3,246,070, which issued to Wooding on Apr. 12, 1966, aconsumable vacuum arc furnace is described. The top electrode (ram) iswater cooled. The bottom electrode (crucible) is also water cooled.Therefore, in the case of any water leakage into the system where moltenmetal is present, a steam explosion is highly probable. Also, asdescribed therein, a continuous process is not possible due to the factthat the consumable electrode cannot be changed without stopping theprocess. In this vacuum arc furnace, due to the use of water cooling inthe crucible, a smelting process that requires a very high energy inputand temperature, for example 11-13 kWhr/kg of silicon at temperaturesabove 1800° C., cannot be economically and efficiently practiced.

In U.S. Pat. No. 4,027,095, which issued to Kishida et al. on May 31,1977, a hermetically sealed arc furnace is disclosed for the productionof steel. As per this arc furnace, the electrode sealing is protectedfrom the furnace heat by means of water cooling. The movement of theelectrodes is provided by a telescopic mechanism of the seal allowingfor upward and downward movement. As per the description of the seal, agraphite electrode is in direct contact with the seal. Since graphitematerials possess notable porosity and poor surface finish, achieving avery high vacuum level cannot be possible.

In U.S. Pat. No. 5,127,468, which issued to Poulsen on Jul. 7, 1992,reference is made to a consumable electrode vacuum arc furnace formelting metal and alloys, particularly titanium and titanium-basealloys. As described, the vacuum furnace cannot run continuously asmelting is continued until the annular marginal area at least begins tomelt and melting is discontinued before the marginal area melts awaycompletely.

Therefore, it would be desirable to provide a sealed electric vacuum arcfurnace that can operate without water-cooling with a consumablemoveable electrode, particularly one made of graphite.

SUMMARY

It would thus be desirable to provide a novel vacuum arc furnace that isprovided with a consumable moveable electrode.

The embodiments described herein provide in one aspect an electric arcfurnace, comprising a (closed) vessel, at least one top electrode, atleast one bottom electrode, the vessel including a top furnace spool anda bottom furnace crucible, the top electrode being adapted to carryelectric current so as to maintain a plasma arc between the topelectrode and the bottom electrode, at least one feeding port adapted tobe displaced between an open position for charging of materials in thevessel and a closed sealed position, at least one exhaust port adaptedfor exhausting furnace gas from the vessel and to be sealed from anexhaust line, and at least one tap hole adapted to be displaced betweenan open position for removing molten material from the furnace crucibleand a closed sealed position.

For instance, the top furnace spool and the bottom furnace crucible areboth refractory-lined.

For instance, the top electrode is made of any suitable material, forinstance of carbon material(s), such as graphite.

For instance, a top electrode assembly is provided externally of thevessel for sealing the top electrode from an outside environment

For instance, a housing is provided atop the furnace spool with the topelectrode extending within the housing and into the vessel.

For instance, the top electrode is sealed from the outside environmentthrough the top electrode assembly, via at least one seal providedbetween lower flanges connecting a lower end of the housing to thevessel, also via at least one seal provided between upper flangesconnecting an upper end of the housing to the top electrode assembly,and also possibly via at least one seal provided between intermediateflanges connecting together sections of the housing.

For instance, a sleeve is provided externally of the top electrode andinternally of the housing.

For instance, the sleeve is located between the top electrode and vacuumseals in the top electrode assembly so that vacuum sealing is onlycarried out on the sleeve.

For instance, the sleeve is made of high duty materials that are suitedfor vacuum sealing, such as steel materials.

For instance, a gap is provided between the sleeve and the topelectrode, whereby the sleeve is adapted to act as a thermal barrierbetween the top electrode and the housing where seals are located.

For instance, the gap is adapted to be maintained under vacuum, heattransfer from the top electrode and surroundings thereof being limitedby forcing heat along the top electrode towards the top electrodeassembly where it is cooled by natural air convection.

For instance, by having the top electrode thermally insulated by thesleeve, commercially available sealing materials can be used for sealslocated exteriorly of the sleeve, sealing materials such as Viton™.

For instance, a cleaning device is provided substantially at a junctionof the furnace spool and the housing for substantially preventingparticulates entrained in the furnace gas from entering the housing.

For instance, the cleaning device is also adapted to remove depositsfrom the top electrode, in each displacement of the top electrode.

For instance, the cleaning device is made of electrically insulatedmaterial, such as ceramics.

For instance, the feeding port is sealed by a seal, made, for example,of a compressible gasket or O-rings, which seal is placed on the feedingport and a cap for blocking the feeding port when charging the vessel isstopped or when a vacuum valve, such as a gate valve, is closed.

For instance, the seal of the feeding port is selected from commerciallyavailable materials, as temperatures at the feeding port are low enough.

For instance, the exhaust port is sealed by a seal, made, for example,of a compressible gasket or O-rings, which seal is placed on the exhaustport and a cap for blocking the exhaust port when desired.

For instance, the seal of the exhaust port is selected from commerciallyavailable materials, as temperatures at the exhaust port are low enough.

For instance, a non-water-cooled vessel flange is provided at a junctionof the furnace spool and furnace crucible and is sealed thereat by avessel seal.

For instance, refractory linings are provided in each of the furnacespool and furnace crucible and inwardly of the vessel seal therebylimiting the temperatures at the vessel seal, whereby the vessel sealdoes not require to be water-cooled.

For instance, the vessel seal is selected from commercially availablesealing materials, such silicone or PTFE.

For instance, a bottom electrode assembly is provided, which includesthe bottom electrode, the bottom electrode including an electricallyconductive extension lead (or rod).

For instance, the bottom electrode assembly is connected to the furnacecrucible by means of the extension rod.

For instance, an electrically conductive lining is provided at a bottomof the furnace crucible, the extension rod being embedded (or buried) inthe conductive lining.

For instance, the electric arc is adapted to be initially formed betweenthe top electrode and the conductive lining by passing electricalcurrent through the extension rod and bottom electrode assembly, thebottom electrode assembly being adapted to be connected to a powersupply.

For instance, the tap hole extends in the furnace crucible above theconductive lining so that the molten material contained in the furnacecrucible can be periodically tapped out through the tap hole.

For instance, the tap hole is blocked during furnace operation by a caplined with a refractory, the cap being sealed by a seal to maintain avacuum or pressure throughout the furnace operation and to avoid escapeof process gases and/or molten materials during the furnace operation.

For instance, the top electrode assembly includes a removable electricalconnector for connecting the top electrode to a power supply and forallowing a new top electrode to be added for compensating forconsumption of a used electrode, when the top electrode is made ofconsumable electrode material, thereby enabling a continuous orsemi-continuous process

For instance, the removable electrical connector is adapted to connectthe top electrode to the power supply via a proper electrical extension,such as copper bus bars.

For instance, the removable electrical connector is electricallyisolated from the vessel by means of at least two high temperatureelectrical insulators, such as machinable material like PEEK orglass-silicon laminate.

For instance, one of the electrical insulators and the removableelectrical connector are sealed by at least upper and lower sealingcomponents, such as O-rings, the lower sealing component being adaptedto sit on a flange attached to the sleeve.

For instance, the sleeve is sealed by means of at least one sealingcomponent, such as a Lip seal or spring-loaded seals, for withstanding adisplacement of the top electrode and a high temperature of the sleeve.

For instance, a guide is provided for ensuring that the removableelectrical connector, the top electrode and the sleeve are aligned andsealing components are well positioned and maintained during theoperation of the furnace, the guide extending between the sleeve and thehousing of the top electrode assembly, and the guide being made forinstance of non-abrasive/self-lubricating materials.

For instance, an anode housing of the bottom electrode assembly isconnected to the furnace crucible by means of a flexible bellows tubeadapted to allow the bottom anode assembly to move slightly withoutaffecting the vacuum sealings.

For instance, due to a high temperature gradient in the furnace crucibleand along the bottom anode assembly, notable expansion/contraction of atleast the extension lead, which experiences a temperature gradient forexample from more than 1800° C. to less than 300° C. in the bottom anodeassembly, is adapted to be accommodated by the bellows tube.

For instance, as the temperature of the furnace crucible increases, theextension lead linearly expands along an axis thereof, thereby pushingthe bottom anode assembly downwardly, with a resulting downwarddisplacement being compensated by the bellows tube for maintaining adesired vacuum level in the vessel.

For instance, the bottom electrode includes an electrical connector thatis attached to a lower end of the extension lead.

For instance, the electrical connector is attached to an upperconductive plate for allowing a good portion of heat transferred fromthe furnace crucible through the extension lead to be dissipated in thebottom electrode assembly exteriorly of the furnace crucible, therebymaintaining an operating temperature of the furnace for keeping sealingcomponents below maximum service temperatures thereof.

For instance, both the electrical connector and the upper conductiveplate are made of highly electrically and thermally conductivematerials, such as copper.

For instance, the bottom electrode assembly includes a cooling deviceadapted to having a cooling medium, such as air, to be blown thereon.

For instance, the cooling device includes finned tubes, for instancemade of copper, which are stacked in a housing for effective heattransfer from the bottom electrode assembly to the cooling air.

For instance, the housing is adapted to confine the finned tubes and todirect a gas coolant, such as air, over fins of the finned tubes.

For instance, the finned tubes are positioned between the upperconductive plate and a lower conductive plate, with hanger rodsconnecting the upper and lower conductive plates.

For instance, the hanger rods are electrically insulated from the lowerconductive plate by means of grommets for maintaining the housingelectrically insulated from the bottom anode assembly.

For instance, the hanger rods not only keep the finned tubes in place,but are also adapted to compress the upper conductive plate towardsvacuum seals for effective tightness and sealing, the vacuum seals 43,such as O-rings, being placed over an insulation ring adapted to act asan electrical disconnector between the bottom anode assembly and afurnace shell.

For instance, the housing is connected to a lower end of the bellowstube.

For instance, the bottom anode assembly is attached to the furnacecrucible via a transition flange mounted to a furnace crucible shell,the bottom electrode including an extended electrically conductive leadattached to the lower conductive plate, the bottom anode assembly beingconnected to a power supply by means of the electrically conductivelead.

For instance, the top electrode and the sleeve are adapted for moving upand down together.

For instance, the top electrode and the sleeve are connected together atupper ends thereof via at least one intermediate component.

For instance, the top electrode and the sleeve are connected together atupper ends thereof via at least the removable electrical connector,whereby the top electrode and the sleeve are adapted for moving up anddown together.

For instance, the furnace is used for the production of produce highpurity silicon (+99.9% purity Si) from its raw material (quartz,quartzite) by carbothermic reduction reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the embodiments described herein and toshow more clearly how they may be carried into effect, reference willnow be made, by way of example only, to the accompanying drawings, whichshow at least one exemplary embodiment, and in which:

FIG. 1 is a schematic vertical cross-sectional view of a consumablevacuum arc furnace in accordance with an exemplary embodiment;

FIG. 2 is an enlarged schematic cross-sectional view of a top electrodeassembly of the consumable vacuum arc furnace of FIG. 1, taken from thedotted circle A of FIG. 1, in accordance with an exemplary embodiment;

FIG. 3 is an enlarged schematic cross-sectional view of a bottomelectrode assembly of the consumable vacuum arc furnace of FIG. 1, takenfrom the dotted circle B of FIG. 1, in accordance with an exemplaryembodiment;

FIG. 4 is an exemplary schematic representation of a temperature profileof the top electrode assembly of FIG. 2 at an operating temperature of1800° C., in accordance with an exemplary embodiment; and

FIG. 5 is an exemplary graph of a temperature profile of the bottomelectrode assembly of FIG. 3 at an operating temperature of 1800° C., inaccordance with an exemplary embodiment.

DESCRIPTION OF VARIOUS EMBODIMENTS

The present subject matter relates to a consumable electrode vacuum arcfurnace and, more particularly, to a direct current consumable electrodevacuum arc furnace, wherein no water cooling is needed to cool downtypically neither the electrodes, nor any other parts of the furnace,including but not limited to the shell, the flanges ports and theelectrical connections of the furnace. Specifically, the present subjectmatter relates to a non-metallic electrode, such as graphite electrodearc furnaces suitable for melting of metals, smelting of metal ores, andmetal oxide to elemental metal where the use of graphite electrodes is acommon practice. The present subject matter renders possible to performa true continuous process of melting and smelting under controlledpressure, which is a key factor for the latter process.

Now referring to FIG. 1, an embodiment is shown of a vacuum electric arcfurnace F, which comprises one consumable electrode and arefractory-lined closed vessel designed to operate at high temperaturesand suitable for melting and smelting processes. The furnace F iscomprised of four main subsections: a top furnace spool 1, a furnacecrucible 2, a furnace top electrode(s) assembly 3, and a furnace bottomelectrode(s) assembly 4. The spool 1 is lined with a refractorymaterial(s) 5, for protection from hot and/or reactive evolving gas andfor maintaining heat within the vessel. The spool 1 is designed to actas a closing cap on top of the furnace crucible 2, and to keep the wholefurnace enclosed.

The furnace crucible 2 is also lined with a refractory materials(s) 6,to maintain the necessary heat for the process and to protect thefurnace shell. Top electrode(s) 7 carries the electric current suppliedby power supply(s), not shown, to the process by maintaining a plasmaarc between the top electrode 7 and a bottom electrode 4 a of the bottomelectrode assembly 4, through an extension lead, or rod, 26. The topelectrode 7 can be made of any suitable material for the specificprocess, which is known to experts in the field. More particularly, itcan be made of carbon material(s), such as pre-baked graphite forsmelting processes, such as silicon production from quartz where carbonis one of the reductants. The use of graphite electrodes is also commonin metal melting processes. The bottom electrode 4 a includes theextension lead 26, a connector 35 and an extended electricallyconductive lead 48.

The top electrode 7, is sealed from the outside environment through thetop electrode assembly 3, by a seal 10 located between a pair of middletop flanges 11, and by a seal 12 located between a pair of bottom topflanges 13. The top electrode 7 is separated from an elongated housing 9by means of a sleeve 8. The sleeve 8 plays an important role in the topelectrode 7 functionality. Firstly, the sleeve 8 is located between thetop electrode 7 and the vacuum seals in the top electrode assembly 3 sothat the vacuum sealing is only done on the sleeve 8 which can be madeof high duty materials proper for vacuum sealing, such as steelmaterials that can be easily machined down to a very precise toleranceand accepted surface finish for high vacuum sealing purposes. Secondly,the sleeve 8 acts as a thermal barrier between the top electrode 7 andthe elongated housing section 9 where the seals are located. This isachieved by a gap 50 provided between the sleeve 8 and the top electrode7, which can be kept under vacuum. This design helps to minimize heattransfer from the top electrode 7 and its surroundings by forcing theheat flows along the top electrode 7 towards the top electrode assembly3 where it is cooled by natural air convection. Having the top electrode7 thermally insulated by the sleeve 8 allows for the use of commerciallyavailable sealing materials for seals 10 and 12, such as Viton™, and forseal 31 of the top electrode assembly 3 (see FIG. 2). Thirdly, the topelectrode 7 and the sleeve 8 are connected at upper ends thereof, viaother components described hereinafter, and the sleeve 8 is connected toa driving device (not shown), such that the top electrode 7 and thesleeve 8 are adapted to move up and down together.

High temperature processing of materials, and particularly in smeltingprocesses, where the electric arc is used, generates dusts made of veryfine particulates. These particulates entrained in the furnace gas, canenter the sleeve 8, and get deposited on the seals 10, 12 and 31. Thiscan result in a reduced vacuum sealing efficiency of the seals in thetop electrode assembly 3 in continuous process. Therefore, a cleaningdevice 14 made of electrically insulated material, such as ceramics, isprovided to block the particulates from entering the sleeve 8 and removedeposits from the top electrode 7, in each displacement of the sleeve 8.

For continuous or semi-continuous processes, charging of materials ispossible through a feeding port(s) 15, which is sealed by a seal 16. Theseal 16 can be, for example, made of a compressible gasket or O-rings,which is placed on the port 15 and a cap, not shown, for blocking theport 15 when feeding is stopped or when a vacuum valve (not shown), suchas a gate valve, is closed. The furnace gas is exhausted through anexhaust port 17, which is sealed from the exhaust line (not shown) by aseal 18. Both seals 16 and 18 can be selected from commerciallyavailable materials since the expected temperature at these locationsare well below the standard limit.

The spool 1 and the crucible 2 are connected by a non-water-cooledflange 19, which is sealed by a seal 20. The refractory linings 5 and 6make it possible to maintain the flange temperature well below 220° C.for process temperatures above 1800° C. At this flange temperature ofbelow 220° C., commercially available sealing materials, such assilicone or PTFE, can be used without the need for water-cooling.

The molten material that is contained in the bottom of crucible 2 in aconductive lining 25 can be periodically tapped out through a taphole(s) 21, which is blocked during the operation by a cap 22 lined witha refractory 23. The cap 22 is sealed by a seal 24 to maintain thevacuum or pressure throughout the process and to avoid escape of processgases and/or molten materials during the furnace operation. The bottomelectrode assembly 4 is connected to the furnace crucible 2 by means ofthe electrically conductive extension rod 26, which is embedded orburied in the electrically conductive lining 25. The electric arc isinitially formed between the top electrode 7 and the conductive lining25 by passing electrical current through the electrically conductiveextension rod 26 and bottom electrode assembly 4, which is connected tothe power supply (not shown).

With reference to FIG. 2, an embodiment is shown wherein the topelectrode assembly 3 of FIG. 1 includes a removable electrical connector27 to connect the top electrode 7 to the power supply via a properelectrical extension, such as copper bus bars. The connector 27 iselectrically isolated from the furnace body by means of two hightemperature electrical insulators 28 and 29, such as that of machinablematerial like PEEK or glass-silicon laminate. The electrical insulator29 and the removable connector 27 are sealed by at least two sealingcomponents 30 (upper sealing component) and 31 (lower sealingcomponent), such as O-rings. The removability feature of the connector27 allows for adding a new electrode to compensate for consumption of anold electrode, in case of consumable electrode material, therebyenabling a continuous or semi-continuous process. The lower sealingcomponent 31 is sitting on a welded flange 32 attached to the sleeve 8.The sleeve 8 is also sealed by means of at least one sealing component33 to withstand the top electrode 7 displacement and the hightemperature of the sleeve 8. The choice of this sealing component 33 isdependent on the level of vacuum to be reached and the leak rate,whereby various sealing components known to experts in the field, suchas Lip seal or spring-loaded seals, can be used. In order to ensure thatthe connector 27, the top electrode 7 and the sleeve 8 are alwaysaligned and sealing components are well placed and maintained during theoperation of the furnace F, a guide 34, which is made ofnon-abrasive/self-lubricating materials, is installed between the sleeve8 and the housing 9 of the top electrode assembly 3. From FIG. 2, it canbe seen that the top electrode 7 is connected to the sleeve 8 by meansof the connector 27, the electrical insulators 28 and 29 and the weldedflange 32.

Now referring to FIG. 3, an embodiment is shown wherein the bottomelectrode assembly 4, as shown in FIG. 1, includes the bottom electrode4 a with the electrical connector 35 thereof being attached to theelectrically conductive extension lead 26 exteriorly of the furnacecrucible 2. The electrical connector 35 is attached to a conductiveplate 37, both to be made of highly electrically and thermallyconductive materials, such as copper. This is because a good portion ofthe heat transferred from the furnace crucible 2 through the conductiveextension lead 26 is dissipated in the bottom electrode assembly 4 andmust be thermally managed to maintain the operating temperature of thefurnace and to keep the sealing components below their maximum servicetemperatures. Therefore, the use of high thermally and electricallyconductive materials allows for the effective gas cooling, such as aircooling, with minimal heat generation by the electrical current whenhigh intensity is applied such that for smelting process. The aircooling is possible by blowing air over finned copper tubes 38, whichare stacked in a pre-defined pattern in a housing 42, as compact aspossible, to maximize the heat transfer rate from the bottom electrodeassembly 4 to the cooling air and minimize space requirements. Thepurpose of the housing 42 is to confine the finned tubes 38 and todirect a gas coolant, such as air, over the fins on the tubes 38. Thefinned-tube housing 42 is electrically isolated by an insulator spacer49. The finned tubes 38 are placed between upper and lower plates 37 and39 with hanger rods 40. The hanger rods 40 are electrically insulatedfrom the plate 39 by use of grommets 41. This is to keep the finned-tubehousing 42 electrically insulated from the bottom anode assembly 4. Thehanger rods 40 not only keep the finned tubes 38 in place, but alsocompress the plate 37 towards vacuum seals 43 for maximum tightness andsealing. The vacuum seals 43, such as O-rings, are placed over aninsulation ring 44, which acts as an electrical disconnector between thebottom anode assembly 4 and the furnace shell.

The anode housing 42 is connected to the furnace crucible 2 by means ofa flexible bellows tube 45. The bellows tube 45 allows the whole bottomanode assembly 4 to move and breathe slightly without affecting thevacuum sealings. Due to the high temperature gradient in the furnacecrucible 2 and along the bottom anode assembly 4, a notableexpansion/contraction of material exposed to high temperature gradientis expected. The main expansion is expected for the extension lead 26,which experiences a huge temperature gradient from more than 1800° C. toless than 300° C. in the bottom anode assembly 4. Therefore, as thetemperature of the furnace crucible 2 increases, the conductiveextension lead 26 linearly expands along its axis, pushing the bottomanode assembly 4 downward. This downward force is then compensated bythe bellows tube 45 to keep the desired vacuum level in the furnace F.The bottom anode assembly 4 is attached to the furnace crucible 2through a transition flange 46, which is welded to a furnace crucibleshell 47. The bottom anode assembly 4 is connected to the power supply(not shown) through the conductive lead 48, which is attached to thelower plate 39.

EXAMPLE 1

In one example, the temperature profile of the top electrode assembly 3in 2-dimensions was simulated for a smelting process (reactiontemperature over 1800° C. in the furnace). No internal cooling wasconsidered. Only external air cooling by natural convection on the topelectrode assembly 3 was considered. The result of this thermal modelingis presented in FIG. 4. The temperature varies between 700° C. at thelowest point (electrode) to 80° C. at the highest point (cap). Thetemperatures at the seals are low enough (<200° C.) to use commerciallyavailable products with no internal cooling required. The temperature ofthe extended copper part that connects to electrical wires or bus bar,is well below 75° C., which is necessary for these types of connections.Therefore, the simulation results indicate that the top electrodeassembly 3 does not need any additional type of cooling and especiallywater cooling.

EXAMPLE 2

In another example, the temperature profile in 1D of the bottom anodeassembly 4 was calculated using forced air for cooling. The hot facetemperature of the furnace bottom was considered at 1800° C., which iswithin the range of a smelting process. The one directional temperatureprofile of the bottom electrode was simulated, and the result of thetemperature profile is depicted in

FIG. 5. It will be apparent that the temperature drop along the axis ofthe bottom anode 4 a is considerable, thereby resulting in a temperatureof below 200° C. at the vacuum sealing points. This indicates a safetemperature for use of commercially available sealing materials, such asViton O-rings.

Therefore, there is thus herein provided:

a non-water-cooled closed electric arc furnace

a non-water-cooled vacuum electric arc furnace

a non-water-cooled consumable electrode vacuum electric arc furnace

a non-water-cooled consumable electrode vacuum eclectic arc furnace forsmelting process at high temperatures

a closed non-water-cooled electric arc furnace suitable for smeltingprocesses of ore and metal oxide to elemental metals

a closed non-water-cooled electric arc furnace suitable for smeltingprocesses of ore and metal oxide to elemental metals with continuousfeeding of smelting material

There is also herein provided a new electrode sealing adapted to allowreaching very high vacuum levels in the electric arc furnace without aneed for water cooling.

There is further herein provided a closed electric arc furnace equippedwith an air-cooled bottom anode system.

There is still further herein provided a vacuum electric arc furnacewith consumable graphite electrode.

There is still further herein provided a sealed continuously fed vacuumfurnace.

While the above description provides examples of the embodiments, itwill be appreciated that some features and/or functions of the describedembodiments are susceptible to modification without departing from thespirit and principles of operation of the described embodiments.Accordingly, what has been described above has been intended to beillustrative of the embodiments and non-limiting, and it will beunderstood by persons skilled in the art that other variants andmodifications may be made without departing from the scope of theembodiments as defined in the claims appended hereto.

1. An electric arc furnace, comprising a (closed) vessel, at least onetop electrode, at least one bottom electrode, the vessel including a topfurnace spool and a bottom furnace crucible, the top electrode beingadapted to carry electric current so as to maintain a plasma arc betweenthe top electrode and the bottom electrode, at least one feeding portadapted to be displaced between an open position for charging ofmaterials in the vessel and a closed sealed position, at least oneexhaust port adapted for exhausting furnace gas from the vessel and tobe sealed from an exhaust line, and at least one tap hole adapted to bedisplaced between an open position for removing molten material from thefurnace crucible and a closed sealed position.
 2. The electric arcfurnace of claim 1, wherein the top furnace spool and the bottom furnacecrucible are both refractory-lined.
 3. The electric arc furnace of anyone of claims 1 and 2, wherein the top electrode is made of any suitablematerial, for instance of carbon material(s), such as graphite.
 4. Theelectric arc furnace of any one of claims 1 to 3, wherein a topelectrode assembly is provided externally of the vessel for sealing thetop electrode from an outside environment.
 5. The electric arc furnaceof claim 4, wherein a housing is provided atop the furnace spool withthe top electrode extending within the housing and into the vessel. 6.The electric arc furnace of claim 5, wherein the top electrode is sealedfrom the outside environment through the top electrode assembly, via atleast one seal provided between lower flanges connecting a lower end ofthe housing to the vessel, also via at least one seal provided betweenupper flanges connecting an upper end of the housing to the topelectrode assembly, and also possibly via at least one seal providedbetween intermediate flanges connecting together sections of thehousing.
 7. The electric arc furnace of any one of claims 5 to 6,wherein a sleeve is provided externally of the top electrode andinternally of the housing.
 8. The electric arc furnace of claim 7,wherein the sleeve is located between the top electrode and vacuum sealsin the top electrode assembly so that vacuum sealing is only carried outon the sleeve.
 9. The electric arc furnace of claim 8, wherein thesleeve is made of high duty materials that are suited for vacuumsealing, such as steel materials.
 10. The electric arc furnace of anyone of claims 7 to 9, wherein a gap is provided between the sleeve andthe top electrode, whereby the sleeve is adapted to act as a thermalbarrier between the top electrode and the housing where seals arelocated.
 11. The electric arc furnace of claim 10, wherein the gap isadapted to be maintained under vacuum, heat transfer from the topelectrode and surroundings thereof being limited by forcing heat alongthe top electrode towards the top electrode assembly where it is cooledby natural air convection.
 12. The electric arc furnace of any one ofclaims 7 to 11, wherein, by having the top electrode thermally insulatedby the sleeve, commercially available sealing materials can be used forseals located exteriorly of the sleeve, sealing materials such asViton™.
 13. The electric arc furnace of any one of claims 5 to 12,wherein a cleaning device is provided substantially at a junction of thefurnace spool and the housing for substantially preventing particulatesentrained in the furnace gas from entering the housing.
 14. The electricarc furnace of claim 13, wherein the cleaning device is also adapted toremove deposits from the top electrode, in each displacement of thesleeve.
 15. The electric arc furnace of any one of claims 13 to 14,wherein the cleaning device is made of electrically insulated material,such as ceramics.
 16. The electric arc furnace of any one of claims 1 to15, wherein the feeding port is sealed by a seal, made, for example, ofa compressible gasket or O-rings, which seal is placed on the feedingport and a cap for blocking the feeding port when charging the vessel isstopped or when a vacuum valve, such as a gate valve, is closed.
 17. Theelectric arc furnace of claim 16, wherein the seal of the feeding portis selected from commercially available materials, as temperatures atthe feeding port are low enough.
 18. The electric arc furnace of any oneof claims 1 to 17, wherein the exhaust port is sealed by a seal, made,for example, of a compressible gasket or O-rings, which seal is placedon the exhaust port and a cap for blocking the exhaust port whendesired.
 19. The electric arc furnace of claim 18, wherein the seal ofthe exhaust port is selected from commercially available materials, astemperatures at the exhaust port are low enough.
 20. The electric arcfurnace of any one of claims 1 to 19, wherein a non-water-cooled vesselflange is provided at a junction of the furnace spool and furnacecrucible and is sealed thereat by a vessel seal.
 21. The electric arcfurnace of claim 20, wherein refractory linings are provided in each ofthe furnace spool and furnace crucible and inwardly of the vessel sealthereby limiting the temperatures at the vessel seal, whereby the vesselseal does not require to be water-cooled.
 22. The electric arc furnaceof claim 21, wherein the vessel seal is selected from commerciallyavailable sealing materials, such silicone or PTFE.
 23. The electric arcfurnace of any one of claims 1 to 22, wherein a bottom electrodeassembly is provided, which includes the bottom electrode, the bottomelectrode including an electrically conductive extension lead (or rod).24. The electric arc furnace of claim 23, wherein the bottom electrodeassembly is connected to the furnace crucible by means of the extensionrod.
 25. The electric arc furnace of any one of claims 23 to 24, whereinan electrically conductive lining is provided at a bottom of the furnacecrucible, the extension rod being embedded (or buried) in the conductivelining.
 26. The electric arc furnace of claim 25, wherein, the electricarc is adapted to be initially formed between the top electrode and theconductive lining by passing electrical current through the extensionrod and bottom electrode assembly, the bottom electrode assembly beingadapted to be connected to a power supply.
 27. The electric arc furnaceof any one of claims 25 to 26, wherein the tap hole extends in thefurnace crucible above the conductive lining so that the molten materialcontained in the furnace crucible can be periodically tapped out throughthe tap hole.
 28. The electric arc furnace of claim 27, wherein the taphole is blocked during furnace operation by a cap lined with arefractory, the cap being sealed by a seal to maintain a vacuum orpressure throughout the furnace operation and to avoid escape of processgases and/or molten materials during the furnace operation.
 29. Theelectric arc furnace of any one of claims 7 to 15, wherein the topelectrode assembly includes a removable electrical connector forconnecting the top electrode to a power supply and for allowing a newtop electrode to be added for compensating for consumption of a usedelectrode, when the top electrode is made of consumable electrodematerial, thereby enabling a continuous or semi-continuous process. 30.The electric arc furnace of claim 29, wherein the removable electricalconnector is adapted to connect the top electrode to the power supplyvia a proper electrical extension, such as copper bus bars.
 31. Theelectric arc furnace of any one of claims 29 to 30, wherein theremovable electrical connector is electrically isolated from the vesselby means of at least two high temperature electrical insulators, such asmachinable material like PEEK or glass-silicon laminate.
 32. Theelectric arc furnace of claim 31, wherein one of the electricalinsulators and the removable electrical connector are sealed by at leastupper and lower sealing components, such as O-rings, the lower sealingcomponent being adapted to sit on a flange attached to the sleeve. 33.The electric arc furnace of any one of claims 7 to 15 and 29 to 32,wherein the sleeve is sealed by means of at least one sealing component,such as a Lip seal or spring-loaded seals, for withstanding adisplacement of the top electrode and a high temperature of the sleeve.34. The electric arc furnace of any one of claims 29 to 32, wherein aguide is provided for ensuring that the removable electrical connector,the top electrode and the sleeve are aligned and sealing components arewell positioned and maintained during the operation of the furnace, theguide extending between the sleeve and the housing of the top electrodeassembly, and the guide being made for instance ofnon-abrasive/self-lubricating materials.
 35. The electric arc furnace ofany one of claims 23 to 28, wherein an anode housing of the bottomelectrode assembly is connected to the furnace crucible by means of aflexible bellows tube adapted to allow the bottom anode assembly to moveslightly without affecting the vacuum sealings.
 36. The electric arcfurnace of claim 35, wherein, due to a high temperature gradient in thefurnace crucible and along the bottom anode assembly, notableexpansion/contraction of at least the extension lead, which experiencesa temperature gradient for example from more than 1800° C. to less than300° C. in the bottom anode assembly, is adapted to be accommodated bythe bellows tube.
 37. The electric arc furnace of any one of claims 35to 36, wherein, as the temperature of the furnace crucible increases,the extension lead linearly expands along an axis thereof, therebypushing the bottom anode assembly downwardly, with a resulting downwarddisplacement being compensated by the bellows tube for maintaining adesired vacuum level in the vessel.
 38. The electric arc furnace of anyone of claims 23 to 28, 36 and 37, wherein the bottom electrode includesan electrical connector that is attached to a lower end of the extensionlead.
 39. The electric arc furnace of claim 38, wherein the electricalconnector is attached to an upper conductive plate for allowing a goodportion of heat transferred from the furnace crucible through theextension lead to be dissipated in the bottom electrode assemblyexteriorly of the furnace crucible, thereby maintaining an operatingtemperature of the furnace for keeping sealing components below maximumservice temperatures thereof.
 40. The electric arc furnace of claim 39,wherein both the electrical connector and the upper conductive plate aremade of highly electrically and thermally conductive materials, such ascopper.
 41. The electric arc furnace of any one of claims 39 to 40,wherein the bottom electrode assembly includes a cooling device adaptedto having a cooling medium, such as air, to be blown thereon.
 42. Theelectric arc furnace of claim 41, wherein the cooling device includesfinned tubes, for instance made of copper, which are stacked in ahousing for effective heat transfer from the bottom electrode assemblyto the cooling air.
 43. The electric arc furnace of claim 42, whereinthe housing is adapted to confine the finned tubes and to direct a gascoolant, such as air, over fins of the finned tubes.
 44. The electricarc furnace of any one of claims 42 to 43, wherein the finned tubes arepositioned between the upper conductive plate and a lower conductiveplate, with hanger rods connecting the upper and lower conductiveplates.
 45. The electric arc furnace of claim 44, wherein the hangerrods are electrically insulated from the lower conductive plate by meansof grommets for maintaining the housing electrically insulated from thebottom anode assembly.
 46. The electric arc furnace of any one of claims44 to 45, wherein the hanger rods not only keep the finned tubes inplace, but are also adapted to compress the upper conductive platetowards vacuum seals for effective tightness and sealing, the vacuumseals 43, such as O-rings, being placed over an insulation ring adaptedto act as an electrical disconnector between the bottom anode assemblyand a furnace shell.
 47. The electric arc furnace of any one claims 42to 46, wherein the housing is connected to a lower end of the bellowstube.
 48. The electric arc furnace of any one of claims 44 to 47,wherein the bottom anode assembly is attached to the furnace cruciblevia a transition flange mounted to a furnace crucible shell, the bottomelectrode including an extended electrically conductive lead attached tothe lower conductive plate, the bottom anode assembly being connected toa power supply by means of the electrically conductive lead.
 49. Theelectric arc furnace of any one of claims 7 to 15, wherein the topelectrode and the sleeve are adapted for moving up and down together.50. The electric arc furnace of claim 49, wherein the top electrode andthe sleeve are connected together at upper ends thereof via at least oneintermediate component.
 51. The electric arc furnace any one of claims29 to 34, wherein the top electrode and the sleeve are connectedtogether at upper ends thereof via at least the removable electricalconnector, whereby the top electrode and the sleeve are adapted formoving up and down together.
 52. The electric arc furnace of any one ofclaims 1 to 51, wherein the furnace is used for the production ofproduce high purity silicon (+99.9% purity Si) from its raw material(quartz, quartzite) by carbothermic reduction reaction.